Some light beam scanning apparatus utilize a beam scanner having a rotable element such as a polygonal mirror or holographic beam scanning disc (hologon) to impart a scanning motion to a stationary light beam. A beam source directs the imagewise-modulated stationary beam onto successive facets of the rotating polygon or hologon. As the stationary beam encounters each new facet, the beam is thereby made to scan a beam receiving medium. Relative cross-scan motion between the write beam and the beam receiving medium allows the recording of plural rasterized image lines so as to form an image frame. However, because the beam scanner has optical or mechanical characteristics that differ from facet to facet, there is an angular variation of the scan beam from line to line. The separation of adjacent line exposures on the beam receiving medium is modulated in an undesirable pattern that is known as banding.
One way to reduce banding is to use a single facet scanner, but this severely reduces the active time that the beam can be used to write. Hence, the most common approach to reduce banding is to locate anamorphic optics in the beam path. Cylindrical and toroidal lenses are often used (cf. L. Beiser, "Laser Scanning Systems", in Laser Applications, Vol 2, Academic Press, pp. 53-159, 1974). However, anamorphic optical systems are complex and costly. An acousto-optic (AO) or electro-optical (EO) deflector may also be located in the beam path to correct the angular errors of the scanning element. Such deflectors, however, are costly and necessitate additional beam-shaping optics. There is accordingly a need for a beam scanning system that incorporates means for effecting angular correction of the write beam on a facet-to-facet basis without incurring the cost and complexity of prior art approaches, especially in the reproduction of continuous tone image data.